[Interpretation of BRAF gene mutation detection by real-time PCR: a study of 8 644 thyroid fine-needle aspiration...

Objective: To study common problems in BRAF gene mutation detection, and conditions for repetition testing using thyroid fine needle aspiration specimens. Methods: A total of 8 644 cases of thyroid fine-needle aspiration specimens at China-Japan Friendship Hospital were collected between February, 2012 and July, 2018. BRAF gene mutation was detected by real-time PCR. Repeat testing was performed in 237 cases when the results were inconsistent with clinical or cytological diagnosis or when uncertain results were obtained. Results: The final positive rates of BRAF mutation was 22.0% (1 897/8 625). Nineteen cases were excluded due to inadequate DNA samples. The average Ct value of internal quality control was 16.061, and the average Ct value of the positive samples was 19.147. Among 237 repeat tests, 51.4% (19/37) continued to have poor DNA quality and 48.6% (18/37) had adequate DNA resulting in 1 positive case and 17 negative cases. In 40 repetition of initial negative cases, results were unchanged. In initial positive cases, 40.4% (40/99) with a difference of Ct value (between BRAF gene and internal quality control) between 8 to 12 turned negative after repetition, 69.8% (37/53) of these cases with a difference of more than 12 turned negative after repetition. The sensitivity and specificity of BRAF mutation were 83.97% and 96.94%, respectively. Conclusions: Difference between BRAF gene Ct value and internal quality control Ct value is recommended as a reliability index for the test result. Cases with a difference greater than 8 should be subjected to repeat testing.